Bug 878010 - Lock screen orientation for whole phone with item in quick settings

Proposed fix for [#878010](https://bugzilla.mozilla.org/show_bug.cgi?id=878010). This adds a setting `screen.lock` which allows you to set a global screen orientation lock for all apps that don't specify an orientation lock themselves.

For now I've chosen the airplane icon for this mode because don't want to spend too much time on a proposal. So to lock orientation choose the second airplane :) .